Apparatus for separation of a liquid from a multiphase fluid flow

ABSTRACT

An apparatus for separation of a liquid from a multi-phase fluid flow flowing through a pipeline, wherein the fluid flow is set in rotation so that it is separated into a central zone ( 5 ) essentially containing gas, and an outer annular zone ( 6 ) essentially containing liquid, and from which the gas and the liquid in the two-zones are discharged via respective outlet means ( 10, 16 ). The apparatus comprises an essentially tubular casing ( 1 ) arranged to constitute a part of the actual pipeline, a spin element ( 4 ) for rotation of the fluid flow being located at the upstream end of the casing ( 1 ). The outlet means for the gas comprises an outlet element ( 10 ) arranged at the downstream end of the casing ( 1 ) and having a central, axially extending passage ( 11 ) for the gas, and an outer surface which, together with the inner surface of the casing ( 1 ), forms an annulus ( 12 ) for the inflow of liquid, a barrier ( 15 ) for the liquid being formed at the downstream end of the element ( 10 ). The outlet means for the liquid comprises an upwards open container ( 16 ) arranged at the downstream end of the casing ( 1 ) and adapted to receive liquid which flows into the annulus ( 12 ) and partly runs down into the container ( 16 ) from the bottom area of the casing ( 1 ) at the container opening, and partly falls into the container from the area at said barrier ( 15 ).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an apparatus for separation of a liquid from amultiphase fluid flow flowing through a pipeline, wherein the fluid flowis set in rotation so that it is separated into a central zoneessentially containing gas, and an outer annular zone essentiallycontaining liquid, and from which the gas and the liquid in the twozones are discharged via respective outlet means.

2. Description of the Prior Art

In offshore recovery of hydrocarbons (oil and gas), the produced fluidsare often transported in relatively long pipelines and risers up fromthe seabed to the relevant production platform. The produced fluidsusually consist of liquid (oil and water) in which gas and vapour aredissolved. In this connection different types of separation equipmentare used for bulk separation of liquid from a flowing gas/vapour phase.

As mentioned in the introduction, it is known to separate a fluid flowinto liquid and gas by the use of cyclone technique. The separationequipment used today is, however, relatively heavy and space-demanding,and is associated with relatively high building costs.

Thus it is an object of the invention to provide a separation apparatusof the relevant type wherein the apparatus has a compact construction atthe same time as it is simple with respect to manufacture, installationand regulation.

SUMMARY OF THE INVENTION

For the achievement of the above-mentioned object there is provided anapparatus of the introductorily stated type which, according to theinvention, is characterised in

that it comprises an essentially tubular casing arranged to constitute apart of the actual pipeline, a spin element for rotation of the fluidflow being located at the upstream end of the casing,

that the outlet means for the gas comprises an outlet element arrangedat the downstream end of the casing and having a central, axiallyextending passage for the gas, and an outer surface which, together withthe inner surface of the casing, forms an annulus for the inflow ofliquid, a barrier for the liquid being formed at the downstream end ofthe element, and

that the outlet means for the liquid comprises an upwards open containerarranged at the downstream end of the casing and adapted to receiveliquid which flows into the annulus and partly runs down into thecontainer from the bottom area of the casing at the container opening,and partly falls into the container from the area at said barrier.

With the present invention there is provided an apparatus making use of“in-line” technology to separate a fluid flow in a pipeline. Theapparatus is based on the cyclone principle and is provided with anaxial spin element simplifying the “in-line” method in that the suppliedfluid flow and the separated gas fraction can flow in the pipelineaxially into and out of the tubular casing. In this manner the casingcan be simply installed in a straight pipeline stretch without anysubstantial modification of the existing pipe geometry.

The apparatus according to the invention can be used as an inletarrangement to scrubbers and separators in order to improve theperformance of such equipment. Further, the apparatus can be used as astand-alone unit in pipes and pipelines in oil/gas wells, in pipelineson shore or on the seabed, or in processing plants on the shore oroffshore.

In most cases the apparatus can be built with the same nominal diameterand specification as for the pipeline in which the separation is carriedout. This will keep the costs down in application of the technology, andwill considerably reduce the complexity of the relevant installations inrelation to conventional separation technology. This will be the casewith installations in new plants and pipelines, but the profit probablywill be even larger when utilising the technology in existing plants andpipelines.

The advantages of an apparatus constructed in accordance with theinvention can be summarised as follows:

1. Low weight in relation to conventional scrubbers and separators orslug catchers.

2. Low building costs in relation to the above-mentioned equipment.

3. The fact that one uses a pipeline as such for the separationapparatus, makes it possible to build the apparatus with very smalldimensions.

4. The apparatus can be built according to the current pipespecification, so that protection equipment does not become necessary,as is the case for conventional pressure tanks in processing plants.

5. The actual separation of liquid from the gas/vapour phase takes placewithout the gas/vapour phase changing main direction. This results inthat the pressure loss through the apparatus can be kept low at the sametime as the separation of liquid takes place.

6. The apparatus can be installed horizontally as well as verticallywith certain construction modifications.

7. The apparatus to a great extent is self-regulating, so that there isno need for complicated regulating means. Nevertheless, control of theapparatus with a regulating means may be appropriate in someapplications.

BRIEF DESCRIPTION OF THE DRAWING

The invention will be further described below in connection with anexemplary embodiment with reference to the drawing of which the onlyFIGURE shows a schematic, axially sectioned side view of an apparatusaccording to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As appears from the drawing, the apparatus (hereinafter also calledliquid separator) according to the invention comprises a cylindricaltubular casing 1 which is intended for connection into a pipeline (notshown), so that the casing constitutes a part (an “in-line” element) ofthe pipeline proper. The casing 1 has an inlet end 2 for the supply of atwo-phase mixture of liquid and gas/vapour, and an outlet end 3 wherethe gas phase leaves the casing 1, in both cases in the axial directionof the casing.

In the inlet end there is arranged a spin element 4 which, with rotationof the element, sets the two-phase mixture in rotation, so that bycentrifugal action one obtains separation of the two-phase mixture intoa gas phase in a central zone 5 in the casing, and a liquid phase in anannular outer zone 6 at the inner surface of the casing.

The spin element normally has the same diameter as the inner diameter ofthe casing 1, as in the shown embodiment. However, this may be departedfrom up or down if it is found to be appropriate for a definiteapplication.

The spin element 4 itself fits snugly to the inner surface of thecasing, to avoid a direct passing of gas/vapour and liquid which woulddisturb the separation process proper downstream of the spin element.The spin element comprises guide vanes 7 changing the direction of thefluid, so that centrifugal forces arise flinging the liquid outwardstowards the casing wall. The pitch angle and design of the vanes mayvary, dependent on the application.

In order to further improve the inlet conditions in the liquidseparator, a mixing element (not shown) of a commercially available typemay be installed upstream of the spin element 4.

As shown in the drawing, the spin element 4 at its downstream end isformed with an aerodynamic, concentric end part 8 which is taperedtowards the downstream end. This end part is provided with a number ofcircumferentially extending, annular lips 9 which are to ensure that thecyclone flow downstream of the spin element 4 gets a pressure profilewhich is as optimal as possible. The lips serve as liquid stopperspreventing liquid from creeping along the root of the spin element intothe “eye” of the cyclone where there are small or no centrifugal forceswhich can fling liquid in the direction towards the casing wall.

The outlet means for the gas in the central zone 5 comprises an outletelement 10 arranged at the downstream end of the casing 1 and having acentral, axially extending passage 11 for the gas, and an outer surfacewhich, together with the opposite inner surface of the casing, define anannulus 12 for the inflow of liquid in the outer zone 6. In the shownembodiment, the outlet element 10 is a tubular element having acylindrical upstream portion 13 and a downstream portion 14 divergingfrom this portion and being sealingly connected to the casing 1, for theformation of a barrier 15 for the liquid at the downstream end of theannulus.

The design of the outlet element 10 can be adapted to the relevantapplication and to the liquid/gas/vapour ratio and the properties of thefluids, in order to obtain an optimum relation between separationefficiency and pressure drop through the liquid separator.

As shown, the outlet means for the liquid comprises an upwards opencontainer 16 which is arranged at the downstream end of the casing 1 andis adapted to receive liquid which flows into the annulus 12 and partlyruns down into the container 16 from the bottom area of the casing atthe container opening, and partly falls into the container from the areaat said barrier 15.

As appears from the drawing, an upper portion of the container 16 and acentral portion of the upstream end of the spin element 4 areinterconnected by means of a line 17 for recirculation of gas which isentrained by liquid running or falling into the container. The spinelement is provided with a central cavity 18 communicating with the line17, and further is provided with a number of openings 19 in the form ofsmall holes or slots for the discharge of recirculated gas from thecavity 18. A valve 20 is connected in the recirculation line 17, forcontrol of the quantity of recirculated gas.

As shown, the inlet opening of the conduit 17 from the container 16 isshielded by means of a partition 21 projecting a distance into thecontainer from the inlet opening thereof, so that liquid is preventedfrom getting into the conduit.

The recirculation of gas is obtained by utilisation of the negativepressure arising at the centre of the cyclone. This recirculation willimprove the liquid drainage out of the casing of the liquid separator.As mentioned, the quantity of recirculated gas can be controlled bymeans of the valve 20, in order to find the optimum operating conditionfor the relevant application. Because of the negative pressure arisingat the inlet of the conduit 17, the recirculation gas will alsocontribute to drawing separated liquid into the container 16.

The gas which is guided out of the casing 1 via the outlet element 10,still has a rotating movement in the central passage 11. In order torepeal the rotating movement, the gas outlet may be provided with anantispin element if this is found to be appropriate for flow-technicalreasons in some applications. In the illustrated embodiment such anelement 22 is arranged at the downstream end of the outlet element 10.

In the illustrated embodiment the bottom 23 of the container is providedwith a liquid outlet pipe 24 in which there is connected a valve 25 forcontrol of the liquid quantity which is delivered from the container andwhich is conducted to a suitable place in the relevant processing plantor production system. The control valve 25 is arranged to be controlledby means of a level controlling unit 26 which is connected to a levelgauge 27 for measuring the liquid level in the container. The levelgauge may be of a suitable conventional type, e.g. a PD meter.

The container 16 for example may be a separator, a scrubber or a T-pipeelement, dependent on the relevant application. The container possiblymay be equipped with a more or less advanced drip catcher, for dryingthe recirculation gas to an appropriate level, dependent on theapplication.

For achieving an optimum monitoring of the liquid separator, this may beequipped with pressure sensors (not shown) before the spin element 4, inthe cyclone body, after the gas outlet element 10 and in the liquidcontainer 16. These sensors may be of a conventional type and willprovide valuable information as to how the liquid separator operates ina definite application and under varying operating conditions. Thesignals from the sensors may be used together with the level measurementin the liquid container to prepare an optimum automated controlalgorithm for a definite application.

In the simplest application of the liquid separator, as for example inthe inlet of a separator or scrubber, there will on the whole not be anyneed for monitoring or control of the apparatus. In such applicationsone will only design the liquid separator in order to function in thebest possible manner within a defined operating area and a defined setof operating conditions.

I claim:
 1. An apparatus for separation of a liquid from a multiphasefluid flow flowing through a pipeline, wherein a fluid flow is set inrotation so that said fluid flow is separated into a central zone (5)essentially containing gas, and an outer annular zone (6) essentiallycontaining liquid, and from which the gas and the liquid in the twozones are discharged via respective outlet means (10, 16), saidapparatus comprising: an essentially tubular casing (1) arranged toconstitute a part of the actual pipeline, a spin element (4) forrotation of the fluid flow being located at the upstream end of thecasing (1), an outlet element (10) arranged at the downstream end of thecasing (1) and having a central, axially extending passage (11) for thegas, and an outer surface which, together with the inner surface of thecasing (1), forms an annulus (12) for the inflow of liquid, a barrier(15) for the liquid being formed at the downstream end of the element(10), and an upwards open container (16) arranged at the downstream endof the casing (1) and adapted to receive liquid which flows into theannulus (12) and partly runs down into the container (16) from thebottom area of the casing (1) at the container opening, and partly fallsinto the container (16) from the area at said barrier (15), wherein anupper portion of the container (16) and a central portion of theupstream end of the spin element (4) are interconnected by means of aline (17) for recirculation of gas entrained by liquid running orfalling into the container (16), the spin element (4) having a centralcavity (18) and being provided with a number of openings (19) for thedischarge of recirculated gas from the cavity (18).
 2. An apparatusaccording to claim 1, characterised in that the outlet element (10) is atubular element having a cylindrical upstream portion (13) and adownstream portion (14) diverging from this portion and being sealinglyconnected to the casing (1), for the formation of said barrier (15). 3.An apparatus according to claim 1, characterised in that an antispinelement (22) is arranged at the downstream end of the gas outlet element(10).
 4. An apparatus according to claim 1, characterised in that avalve (20) for control of the quantity of recirculated gas is connectedin the recirculation line (17).
 5. An apparatus according to claim 1,characterised in that the spin element (4) at its downstream end isformed with an aerodynamic, concentric end part (8).
 6. An apparatusaccording to claim 5, characterised in that the spin element (4) at itsdownstream end is provided with a number of circumferentially extending,annular lips (9) serving as liquid stoppers.
 7. An apparatus accordingto claim 1, characterised in that the container (16) in its bottom areahas a liquid outlet pipe (24) in which there is connected a controlvalve (25) for the control of delivered liquid quantity from thecontainer.
 8. An apparatus according to claim 7, characterised in thatthe control valve (25) is arranged to be controlled by means of a levelcontrolling unit (26) connected to a level gauge (27) measuring thelevel of liquid in the container.
 9. An apparatus for separation of aliquid from a multiphase fluid flow flowing through a pipeline, whereina fluid flow is set in rotation so that said fluid flow is separatedinto a central zone (5) essentially containing gas, and an outer annularzone (6) essentially containing liquid, and from which the gas and theliquid in the two zones are discharged via respective outlet means (10,16), said apparatus comprising: an essentially tubular casing (1)arranged to constitute a part of the actual pipeline, a spin element (4)for rotation of the fluid flow being located at the upstream end of thecasing (1), an outlet element (10) arranged at the downstream end of thecasing (1) and having a central, axially extending passage (11) for thegas, and an outer surface which, together with the inner surface of thecasing (1), forms an annulus (12) for the inflow of liquid, a barrier(15) for the liquid being formed at the downstream end of the element(10), and an upwards open container (16) arranged at the downstream endof the casing (1) and adapted to receive liquid which flows into theannulus (12) and partly runs down into the container (16) from thebottom area of the casing (1) at the container opening, and partly fallsinto the container (16) from the area at said barrier (15), wherein thespin element (4) has a downstream end formed with an aerodynamic,concentric end part (8), said downstream end being further provided witha number of circumferentially extending, annular lips (9) serving asliquid stoppers.